Static mixer for an exhaust gas system of an internal combustion engine-driven vehicle, in particular motor vehicle

ABSTRACT

The invention relates to a static mixer for an exhaust gas system of an internal combustion engine-driven vehicle, with a plurality of flow guide elements which influence the flow of an exhaust gas stream and which are inclined at a given angle relative to the mixer plane and are held in the exhaust gas channel by means of at least one retaining strip. According to the invention the at least one retaining strip is made resilient at least in partial regions and/or is elastically supported in the plane of the mixer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. 371 National Stage of PCT/EP2008/008436filed on Oct. 7, 2008, which claims priority from German PatentApplication No. 10 2007 048 558.3 filed on Oct. 9, 2007, the entiredisclosures of which are hereby incorporated by reference.

The invention relates to a static mixer for an exhaust gas system of aninternal combustion engine-driven vehicle.

BACKGROUND OF THE INVENTION

It is generally known that, in conjunction with exhaust emission controlsystems for reducing nitrogen oxide emissions, so-called selectivecatalytic reduction (SCR) is used in which NOx conversion in a leanatmosphere is achieved by means of specially tuned catalytic converters.To reduce NOx, a suitable reducing agent is introduced into the exhaustgas flow in order to obtain final products such as N₂, CO₂ and H₂O. Forexample, ammonia or urea is used as the reducing agent in concert withactive SCR catalytic converters. For mixing of the reducing agent withthe exhaust gas, a static mixer is conventionally used, by means ofwhich the desired distribution of the reducing agent in the exhaust gasflow for efficient exhaust emission control is to be achieved.

U.S. Pat. No. 5,489,153 already discloses a generic static mixer for aflow channel which has a plurality of so-called deflection elements inthe flow channel. The deflection elements here are arranged in rows on arectangular supporting grid. By means of this static mixer, the incomingflow is to be deflected by the deflection elements in differentdirections, the deflection elements generating a transverseflow—relative to the primary direction of flow—in the individualopenings of the supporting grid. Especially effective mixing is therebyto be achieved by the production of swirls, in particular by theformation of rotating vortices. But the problem in conjunction with astatic mixer of this type having a rectangular grid structure is thatcracks and failures in the supporting grid region of the mixer can occurat very high exhaust gas temperatures and/or during temperature changeswith large gradients.

Therefore, the object of this invention is to provide a static mixer foran exhaust gas system of an internal combustion engine-driven vehicle,in particular a motor vehicle, by means of which the risk of mixerdamage is to be reduced in a structurally simple and operationallyreliable manner.

SUMMARY OF THE INVENTION

According to the invention, the at least one retaining strip is maderesilient at least in partial regions and/or is elastically supported inthe plane of the mixer. With this configuration, temperature-inducedstresses due to material expansion and thus failures of the mixer can beprevented in a manner which is simple in terms of construction andproduction technology, since the resilient retaining strip areas canreversibly equalize the expansions.

Preferably, the at least one retaining strip is made curved to formresilient regions in given regions of the retaining strip; inparticular, the regions of curvature are each formed by a retainingstrip region which is curved in an S shape (S-turn). With these curvedretaining strips a rectangular grid arrangement, as is the case in thegeneric prior art, is advantageously avoided. As tests by the inventorshave shown, especially with the curved execution of the retaining stripsor individual regions of the retaining strips, mixers can be made withwhich elastic expansion equalization, especially at high exhaust gastemperatures, and thus the risk of damage to the static mixer, can begreatly reduced.

Especially preferably, there are several retaining strips which run indifferent directions, preferably more or less transversely to oneanother and which thus are arranged in the mixer plane such that atleast one of the retaining strips is fixed with at least one attachmentregion, in particular one end region of the retaining strip, on anotherretaining strip. Specifically, according to one preferred configurationit is provided that at least one retaining strip is arranged as anintermediate retaining strip between two further spaced retainingstrips, which preferably run essentially transversely thereto asattachment retaining strips; in particular, said retaining strip isfastened there with the end regions of the retaining strips. In thisconnection, linking of at least one retaining strip to at least oneother retaining strip in the curvature region is especiallyadvantageous, especially in a roof-shaped or hat-shaped spring convexitythereof. In this way especially low-stress linking of retaining stripsis advantageously made available, with which temperature-inducedexpansions and material deformations can be outstandingly accommodatedand equalized.

Furthermore, the at least one intermediate retaining strip according toone embodiment which has been strength-optimized thermomechanically canbe linked to the two opposite retaining strip end regions in onecurvature region, especially a roof-shaped or hat-shaped springconvexity of the spaced attachment retaining strips. Preferably, thecurvature region, especially the spring recess of each of the twoattachment retaining strips to which at least one intermediate retainingstrip is linked, has a given gap distance from a mixer ring of thestatic mixer or an exhaust gas channel wall.

The attachment retaining strips are moreover made here preferably asidentical parts; this leads to reduction of the diversity of componentsand to cost savings. This is detailed below in conjunction with anotheraspect which is essential for the invention.

According to this aspect, there are preferably several, especially twogroups of retaining strips which are different with respect to theconfiguration of the retaining strips, at least one of these groups ofretaining strips having a plurality of retaining strips which are madeas identical parts within the respective group of retaining strips. Theretaining strips of the different groups of retaining strips can then bearranged in a given configuration in the mixer plane. It is especiallypreferably provided that each of the groups of retaining strips has aplurality of retaining strips which are made as identical parts withinthe group of retaining strips.

With this type of configuration of the static mixer, a static mixer canbe implemented with a structure which is simple in terms of productiontechnology and component engineering, since production costs can beadvantageously reduced by making identical parts. By providing several,especially two different groups of retaining strips, moreover, it can beeasily ensured that different desired configurations for a static mixercan be provided. In particular, these mixers can thus be configured in aform with which the above-described elastic expansion equalization,especially at high exhaust gas temperatures, and thus the risk of damageof the static mixer, can be significantly reduced.

According to one preferred specific configuration, a first group ofretaining strips has a plurality of retaining strips which are made asidentical parts and which have several single-vane guide vanes which arespaced apart from one another as flow guide elements. Especiallypreferably in this connection, it is provided that the guide vanes areall arranged on the same side of the mixer plane and thus project awayfrom this side of the mixer plane. On this side of the mixer plane theguide vanes, however, project in alternation in opposite directions,inclined at a given angle relative to the mixer plane. The single-vaneguide vanes are preferably made plate-shaped and/or blade-shaped.Especially good and effective mixer results can be achieved with thismixer geometry.

According to one specific configuration the retaining strips are heldspaced apart and parallel to one another in the mixer plane so that theindividual guide vanes of the retaining strips lie behind one anothersuch that they form several rows of guide vanes in the mixer plane and,as explained above, preferably without a rectangular grid structure ofthe retaining strips. The individual guide vanes of the retaining stripspreferably lie behind one another such that the individual rows of guidevanes point alternately in opposite directions. In this way outstandingmixer results can be achieved.

One configuration of the retaining strips of a second group of retainingstrips, which configuration is suitable for this specific embodiment ofthe first group of retaining strips, calls for several retaining stripsof this second group of retaining strips to run essentially transverselyto the retaining strips of the first group of retaining strips, theseretaining strips of the second group of retaining strips preferablyhaving such a number of single-vane guide vanes consisting of flow guideelements at such positions that the guide vane gaps in an edge region ofthe mixer plane can be closed in the rows of guide vanes which areformed by the guide vanes of the retaining strips of the first group ofretaining strips; i.e., the guide vanes of the retaining strips of thesecond group of retaining strips thus form a component of the rows ofguide vanes.

The retaining strips are fastened preferably by means of a spot weld,either on a mixer ring or on an exhaust gas channel wall of the exhaustgas line.

In particular, for preliminary fixing or premounting of the mixer, theretaining strips according to one especially preferred configuration canmoreover be connected to one another in their crossing regions by aslip-in slot connection.

Likewise, the retaining strips can be fixed beforehand by means of aslip-in slot connection or other catch fastening on a mixer ring so thatthey can be provisionally fastened, for example, by welds.

A metal or sheet metal material is conventionally used as the preferredmaterial for such a static mixer.

The invention is detailed below using the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a top view of a static mixer according to theinvention,

FIG. 2 shows a rear view of the static mixer as shown in FIG. 1,

FIG. 3 schematically shows one version of a retaining strip of a firstgroup of retaining strips, and

FIG. 4 schematically shows one version of a retaining strip of a secondgroup of retaining strips.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 schematically shows a top view of the static mixer 1 according tothe invention which, as is shown especially in a combined examination ofFIGS. 3 and 4, is made of three retaining strips 2 of a first group ofretaining strips, which strips 2 are made as identical parts, and of tworetaining strips 3 of a second group of retaining strips, which strips 3are made as identical parts, and which are held in a mixer ring 4 of thestatic mixer in a manner which is to be detailed below.

As can be taken from FIG. 4, the retaining strips 2 each have anessentially S-shaped curvature, viewed in the longitudinal direction ofthe retaining strips there being several single-vane, plate-like guidevanes 5 which are spaced apart from one another. These guide vanes 5each project from the same side of the retaining strips 2 and thus, inthe mounted state, as is apparent from FIG. 1, from the same side of themixer plane, the individual guide vanes viewed in just the longitudinaldirection of the retaining strips pointing in alternation in theopposite direction and being inclined at a given angle relative to themixer plane.

The retaining strips 3 of the second group of retaining strips, whichare shown in FIG. 3, are likewise made curved and have a hat-shapedconvexity 6 approximately in the middle region—relative to thelongitudinal direction of the retaining strips. In an end region of theretaining strip 3, which is the left region in the plane of FIG. 3,there is furthermore a guide vane which is made plate-shaped and whichis inclined likewise at a given angle.

As is apparent especially from FIG. 1 at this point in concert with FIG.2, the retaining strips 2 of the first group of retaining strips arespaced apart from one another in the mounted state and are alignedrunning essentially parallel to one another such that the individualguide vanes 5 in the mixer plane formed by the mixer ring 4 form rows 8,9, 10, and 11 of guide vanes, the guide vanes of the retaining strips 2of each row 8, 9, 10, 11 of guide vanes lying behind one another andbeing aligned or inclined pointing in the same direction.

As can furthermore be taken from FIGS. 1 and 2, this yields rows 8, 9,10, 11 of guide vanes, which likewise point in alternation in oppositedirections due to the special configuration of the retaining strips 2together with the guide vanes 5 which are located thereon and whichpoint in the opposite direction, such that the rows of guide vanes whichare directly adjacent to one another each have guide vanes 5 which pointin the opposite direction.

Conversely, the retaining strips 3 (indicated in FIGS. 1 and 2 by thickblack lines and crosshatched guide vanes) of the second group ofretaining strips are mounted running essentially transversely to theretaining strips 2 of the first group of retaining strips in the mixerring 4, the two retaining strips 3 being arranged offset against oneanother and rotated 180° in the mixer plane which is formed by the mixerring 4 such that the convexities 6 end with a given gap distance 12 infront of the mixer ring 4. As can further be taken from FIGS. 1 and 2,by this arrangement of the retaining strips 3 their guide vane 7 travelsinto the guide vane gaps 13, 14 which are made by the configuration ofthe retaining strips 2 together with their guide vanes 5, as dictated bythe design, so that the guide vanes 7 of the retaining strips 3“seamlessly” join the rows 9, 10 of guide vanes and complete these rowsof guide vanes.

As can further be taken from FIGS. 1 and 2, the middle retaining strip 3is fastened with the free ends in the region of the convexities 6, forexample by welding, while the free ends of the remaining retainingstrips 2, in the same manner as the free ends of the retaining strips 3,are connected to the inside of the mixer ring 4 by means of spot welds,for example.

As can further be taken from FIGS. 3 and 4, on the retaining strips 3there are moreover slotted recesses 15, 16, and 17 which accommodate andsurround the correspondingly assigned regions of the retaining strips 2,as a result of which they are connected to one another in the form of aslip-in connection and can be, for example, easily fixed and mountedbeforehand. Moreover, it is ensured in this way that the guide vanes 5,7 of the retaining strips 2, 3 in the mounted state of the mixer 1 lieessentially in the same horizontal plane.

The invention claimed is:
 1. A static mixer for the exhaust system of aninternal combustion engine, comprising: a circular member; a pair ofspaced, identically configured first strips disposed in a stratum ofsaid circular member, each having a base section provided with anundulating configuration and a single vane, said single vane beingdisposed at an end thereof and at an angle relative to the base sectionthereof, and the ends of the base section being secured to said circularmember; and a set of spaced identically configured second stripsdisposed in said stratum, each transversely relative to said firststrips, having undulating configurations, wherein one of said secondstrips interconnects said first strips and is provided, with a set ofspaced vanes alternatively projecting laterally at angles relative to abase section thereof; another one of said second strips is spaced on oneside of said one second strip interconnecting said first strips and isprovided with a set of spaced vanes alternatively projecting laterallyat an angle relative to a base section thereof and interleaving thevanes of said one second strip and the vane of one of said first strips;and a further one of said second strips is spaced on the other side ofsaid one second strip interconnecting said first strips and is providedwith a set of spaced vanes alternatively projecting laterally at anglesrelative to a has section thereof and interleaving the vanes of said onesecond strip and the vane of the other of said first strips.
 2. Thestatic mixer according to claim 1 wherein each of said first strips isprovided with projecting, intermediate curved portions to which said oneof said second strips is connected.
 3. The static mixer of claim 1wherein the connections of said strips together includes a slit providedin the base section of one of said slits and a portion of the basesection of another one of said strips being inserted into said slot. 4.The static mixer according to claim 1 wherein said circular member andsaid strips are formed of a metal and said first strips are spot weldedto said circular member.